1. Field of the Invention
The present invention relates to a turning tool for producing a polishing pad made of a resin material and usable in the fabrication of semiconductor devices, especially for chemical mechanical polishing (CMP) executed for planarizing surfaces of semiconductor wafers or devices. The present invention further relates to a polishing pad effectively formed by using the turning tool, and an apparatus and a method of producing such a polishing pad by utilizing the turning tool.
2. Description of the Related Art
In the semiconductor fabrication processes, a substrate, e.g., a silicon wafer, may undergo multiple masking, etching, implantation, and dielectric and conductor deposition processes, to thereby form a lamination of various kinds of thin layers such as metallic layers and insulative layers. Between each processing steps, it is usually necessary to polish or planarize an outer or upper most surface of the wafer to obtain a substrate surface having a high degree of planarity. Chemical mechanical polishing (hereinafter referred to as “CMP”) is one of known methods of planarization. CMP typically involves placing the wafer mounted on and rotated about an axis of a carrier against a polishing pad mounted on and rotated about an axis of a platen, and pushing the wafer against the polishing pad while supplying a polishing slurry at an interface between the upper most surface of the wafer and the polishing pad. The polishing slurry consists of fine abrasive particles and suitable kind of liquid in which the abrasive particles are dispersed. Typically, the polishing pad is made of a foamed rigid-resin material, so that a surface of the polishing pad has a cellular structure of independent-cell type in which cells are independent of each other or of open-cell type in which cells are communicated with each other, in order to facilitate conditioning of the slurry distribution between the wafer and the polishing pad.
Namely, the polishing pad for CMP is required to be capable of evenly distributing the slurry over a substantially entire area of the upper most surface of the wafer that is to be polished, while preventing a stay or clogging of the slurry at a local portion of the upper most surface of the wafer. The polishing pad for CMP is further required to be capable of promoting renewal of the slurry.
To meet these requirements, conventionally employed polishing pads for CMP are arranged to have polishing surfaces formed with respective predetermined patterns, e.g., a pattern of recess or a pattern of checked grooves intersecting at right rights. After a number of polishing runs, the polishing pad having the pattern of recesses may suffer from variation of diameter of the recesses, whereby the pad suffers from difficulty in exhibiting a desired chemical mechanical polishing effect with high stability. In the case of the polishing pad having the pattern of checked grooves, a polishing condition is likely to vary in the radial direction of the polishing pad, whereby the pad suffers from a high tendency of occurrence of uneven wearing of its surface, resulting in uneven polishing.
Another known example of conventionally employed polishing pad for CMP is disclosed in US Patent Publication Nos. U.S. Pat. No. 5,921,855 and U.S. Pat. No. 5,984,769. The disclosed polishing pad is provided with a plurality of annular grooves open in its polishing surface. The plurality of annular grooves are arranged in a generally concentric or coaxial relationship with each other, and are dimensioned to have a width of not smaller than 0.38 mm and a depth of not smaller than 0.51 mm, and are uniformly spaced with a pitch of 2.29 mm in a radial direction of the polishing pad. However, the disclosed polishing pad suffers from inherent structural problems, namely, difficulty in forming grooves extending in a circumferential direction in the polishing pad and difficulty in ensuring a sufficient dimensional accuracy of the grooves.
More specifically described, the annular grooves may be formed on the polishing surface of the polishing pad by embossing with a die, or alternatively may be formed by milling with a saw blade on a mill. In the former case, each of the formed annular grooves is prone to have a dull shape, especially at its open-end edge portions, so that the width of the groove varies in its depth direction. This causes undesirable variation of the groove width, especially when the polishing surface of the polishing pad is worn or is conditioned by the dressing process, resulting in unstable polishing conditions. In the latter case, since the annular grooves are formed by milling of the saw blade on the mill, the formed annular grooves is likely to extend straightly to some extent, making it difficult to form a groove having a small width and a small radius of curvature. This makes it impossible to form a desired polishing pad in which annular grooves having a relatively small width are formed on a radially inner portion of its polishing surface as well as a radially intermediate and a radially outer portion of its polishing surface. In view of a recent tendency of employing a large-diameter wafer, e.g., a wafer having a diameter within a range of 200 mm–300 mm or more, the presence of useless area in the radially inner portion of the polishing surface of the polishing pad undesirably causes an enlargement in size of the polishing pad. Therefore, the problem of the radially inner useless area of the polishing pad becomes very significant.
Alternatively, the annular grooves may possibly be formed by turning with a turning tool. However, since the polishing pad is formed of a specific material having somewhat elasticity, e.g., a foamed rigid-resin material, it is significantly difficult to cut an annular groove having a relatively small width and having a relatively small radius of curvature into the polishing pad, with high dimensional accuracy. In the light of the physical property of the polishing pad, conventionally available tool for cutting a work piece made of metal or a rigid-resin material, are not suitable to cut the polishing pad. For instance, the tools for cutting the metallic or rigid-resin working piece are likely to interfere with the walls of each groove, thereby possibly producing burrs or other defects in the walls of the grooves. Thus, the conventionally available tools are incapable of cutting the small-width and small-radius grooves into the surface of the polishing pad having the somewhat elasticity, like the foamed rigid-resin members.
Moreover, the conventionally employed polishing pad disclosed in the above-mentioned U.S. Patents has the generally concentric annular grooves that have a relatively large width and are uniformly spaced at the relatively large pitch. Further, the disclosed polishing pad includes a backside pad made of a compressed felt fibers leached with urethane, which has an elasticity larger than that of the polishing pad and which is fixed the backside of the urethane pad. Thus, the disclosed polishing pad is mounted on a platen of an optional CMP system via the backside pad. This type of conventional polishing pad has been developed to be applied to planarization of a substrate having multilevel interconnections in which metallic interconnect has a width of 0.25 μm, that is a most advanced technology at the time when applications for the above-mentioned U.S. Patents were filed (i.e., 1997–1998). Namely, the type of polishing pad has been developed to provide the substrate surface having a planarity at a level of 0.3 μm. In the light of the fact that the substrates having multilevel interconnections whose metallic interconnect has a width approximately of 0.18 μm, 0.15 μm and 0.1 μm dominate the recent market, it is apparent that the CMP is now required very sophisticated techniques, i.e., to provide the substrate surface having a high planarity at a level of 0.25 μm or lower. Thus, the conventional polishing pad disclosed in the above U.S. Patents is insufficient for ensuring currently required polishing accuracy and polishing efficiency, and accordingly is unsuitable to be used for CMP for a planarization of a currently developed substrate of multilevel interconnection, which includes interconnect metal layers made of a soft cupper or gold.
In the conventional polishing pad disclosed in the above-indicated U.S. Patents, the grooves having a relatively large width and the backside pad cooperate to allow a deformation of the polishing surface, whereby the polishing surface of the polishing pad is likely to be deformed according to peaks and valleys in a surface of a substrate to be polished, i.e., along with topography of upper most surface of the substrate. However, this surface deformation mechanism of the conventional polishing pad is insufficient to keep pace with the currently required level of polishing accuracy. In addition, the use of the backside pad, which is formed differently from the polishing pad, evidently has pushed up a manufacturing cost of the polishing pad.